Re: End to End VoIP delay calculation

[Martin Mathieson <martin.r.mathieson () googlemail com>]

There is the RTCP roundtrip network propagation delay.  If the necessary
reports are present and properly formatted, there will be an expert info
item for any calculations that may be made. You will need to enable this
calculation in the RTCP dissector preferences.

Here is the extract from RFC 3550, section 6.4.1, that describes how the
calculation should be done:

delay since last SR (DLSR): 32 bits
      The delay, expressed in units of 1/65536 seconds, between
      receiving the last SR packet from source SSRC_n and sending this
      reception report block.  If no SR packet has been received yet
      from SSRC_n, the DLSR field is set to zero.

      Let SSRC_r denote the receiver issuing this receiver report.
      Source SSRC_n can compute the round-trip propagation delay to
      SSRC_r by recording the time A when this reception report block is
      received.  It calculates the total round-trip time A-LSR using the
      last SR timestamp (LSR) field, and then subtracting this field to
      leave the round-trip propagation delay as (A - LSR - DLSR).  This



Schulzrinne, et al.         Standards Track                    [Page 40]

RFC 3550                          RTP                          July 2003


      is illustrated in Fig. 2.  Times are shown in both a hexadecimal
      representation of the 32-bit fields and the equivalent floating-
      point decimal representation.  Colons indicate a 32-bit field
      divided into a 16-bit integer part and 16-bit fraction part.

      This may be used as an approximate measure of distance to cluster
      receivers, although some links have very asymmetric delays.

   [10 Nov 1995 11:33:25.125 UTC]       [10 Nov 1995 11:33:36.5 UTC]
   n                 SR(n)              A=b710:8000 (46864.500 s)
   ---------------------------------------------------------------->
                      v                 ^
   ntp_sec =0xb44db705 v               ^ dlsr=0x0005:4000 (    5.250s)
   ntp_frac=0x20000000  v             ^  lsr =0xb705:2000 (46853.125s)
     (3024992005.125 s)  v           ^
   r                      v         ^ RR(n)
   ---------------------------------------------------------------->
                          |<-DLSR->|
                           (5.250 s)

   A     0xb710:8000 (46864.500 s)
   DLSR -0x0005:4000 (    5.250 s)
   LSR  -0xb705:2000 (46853.125 s)
   -------------------------------
   delay 0x0006:2000 (    6.125 s)

           Figure 2: Example for round-trip time computation






On Thu, Nov 26, 2009 at 2:48 AM, Martin Visser <martinvisser99 () gmail com>wrote:

> As RTP in each direction is unacknowledged (you have a unidirectional
> stream going each direction) there is no way to determine end-to-delay from
> that. I think the best you can do is look at the SIP request/response time
> as an estimate.
>
> Regards, Martin
>
> MartinVisser99 () gmail com
>
>
> On Wed, Nov 25, 2009 at 4:31 AM, capricorn 80 <
> cool_capricorn80 () hotmail com> wrote:
>
> >  Hi!
> >
> >   (Sorry for repeating my question)
> >
> >  I am looking to calculate the end-to-end delay between two soft
> > phone/hard phone. I have asterisk server and configured ntp server on the
> > same machine and synchronized it with ntp pool.
> >
> >  I have seen that Wireshark can be used to check the jitter. But I am not
> > sure how can i calculate the end to end.
> >
> > May be this is not related to the mailing list topic but please help me if
> > anyone has some information.
> >
> > Regards,
> >
> >
> > ------------------------------
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